Animal parts, such as ground hooves, feathers and toe nails, have been used for making food products. For example, U.S. Pat. No. 4,378,311 to Retrum discloses a method for making food products by hydrolyzing keratinaceous material such as ground up hooves and toe nails. The keratinaceous material is processed by steam hydrolysis. Other methods of hydrolysis, including enzymatic, acid or alkyl hydrolysis are mentioned as unsuitable alternatives because these methods are either too expensive or are destructive to essential amino acids. U.S. Pat. Nos. 4,497,733, 4,286,884 and 4,231,926 to Retrum relate to apparatus for practicing the method of U.S. Pat. No. 4,378,311.
U.S. Pat. No. 4,163,804 to Meyer et al. discloses a puffable, thermoplastic composition derived from animal parts such as ground up animal hooves and a method for producing the same. The method includes drying the raw animal parts to a moisture content between 10% and 25%, grinding up the animal parts and mechanically defatting those parts to a fat content of less than 18%, macerating the defatted particles in an extruder at temperatures between 200.degree. F. and 325.degree. F. under sufficient pressure to cause gelation of the particles and to form a thermoplastic moldable mass, extruding the moldable mass into a shape-sustaining extruded form, cooling the extruded form to below 215.degree. F. and cutting the cooled form into multiple pellets. The multiple pellets are then puffed in hot oil to at least twice the unpuffed volume. Alternatively, the pellets may be thermo formed into a decorative shape for example, a chewable dog bone. U.S. Pat. No. 4,262,028, Meyer et al. discloses essentially the same process with the additional step of combining starch with the ground animal parts prior to extruding, frying and molding.